Hydraulic accumulator with floating piston

ABSTRACT

A hydraulic accumulator cylinder encloses an elastically compressible and expansible gas cushion separated from the hydraulic fluid by a floating piston having sealing and guiding rings. The cylinder has one end wall formed with a substantially central hydraulic fluid inlet and outlet opening, the inner surface of this one end wall defining a bowl shape concavity. An additional ring on the piston constitutes a dirt stripper, and the face of the piston toward the one cylinder end wall is formed with a frustoconical protrusion which, when the maximum amount of fluid has been withdrawn from the cylinder, enters the opening. The piston is formed with an annular bearing surface around the protrusion and engageable with a stationary sealing ring on a countersurface in the concavity, the sealing ring acting as a seal only when the piston is pressed against the countersurface by the gas pressure. In this position of the piston, the piston and the one cylinder end wall define an annular chamber in which there remains a residual amount of fluid serving as a liquid barrier against the gas enclosed in the cylinder.

United States Patent Primary Eicaminer-l-lerbert F. Ross Att0rneyMcGlew and Toren ABSTRACT: A hydraulic accumulator cylinder encloses an elastically compressible and expansible gas cushion separated from the hydraulic fluid by a floating piston having sealing and guiding rings. The cylinder has one end wall formed with a substantially central hydraulic fluid inlet and outlet opening, the inner surface of this one end wall defining a bowl shape concavity. An additional ring on the piston constitutes a dirt stripper, and the face of the piston toward the one cylinder end wall is formed with a frustoconical protrusion which, when the maximum amount of fluid has been withdrawn from the cylinder, enters the opening. The piston is formed with an annular bearing surface around the protrusion and engageable with a stationary sealing ring on a countersurface in the concavity, the sealing ring acting as a seal only when the piston is pressed against the countersurface by the gas pressure. In this position of the piston, the piston and the one cylinder end wall define an annular chamber in which there remains a residual closed in the cylinder.

HYDRAULIC ACCUMULATOR WITH FLOATING PISTON BACKGROUND OF THE INVENTION Before a hydraulic accumulator cylinder of the type including a floating piston is placed in operation, it is filled with compressed nitrogen, usually at one-third of the greatest operating pressure to be expected, which means it is filled at a pressure of 80 at.abs. if the operating pressure is 240 at.abs. This is the so-called fill pressure of the accumulator. When the hydraulic equipment to which the accumulator is connected is placed in operation, the pressure in the fluid supply line rises to the operating pressure and the fluid flows into the accumulator, pushing the piston ahead of it, until the enclosed gas has the same pressure as the fluid efi'ective on the other side or face of the piston.

This pressure usually changes as a function of the working cycle, so that the piston changes its position constantly, during operation, in vibratory motion. The deflections of the piston depend upon the amount of hydraulic fluid flowing out of the accumulator and into the accumulator, and its central position is determined by the mean operating pressure. If the mean operating pressure drop, for any reason, to a value of the order of the mentioned fill pressure, the piston will move to the vicinity of the end wall of the cylinder on the fluid side. It may then happen, when more fluid is withdrawn, that the piston, in its vibratory motion, hits the end wall, thus impairing the safety of operation.

This danger exists particularly when large amounts of fluid are demanded from the accumulator at a small pressure drop, for example, in hydraulic presses or hydraulic lifting devices. In such cases, the accumulator will not be prefilled to onethird of the operating pressure to be expected, but rather to two-thirds of the expected operating pressure, which means a pressure of I60 at.abs. in the selected example. The piston is then forced right from the start to perform its vibratory motions in the vicinity of the end wall of the cylinder on the fluid side of the piston, and the danger of the piston impacting against the end wall is very great.

Another disadvantage of known hydraulic fluid accumulators, of the floating piston type, is that the gas filling escapes from the accumulator after a certain period of operation. This makes it necessary to check the gas pressure at regular intervals, and to replenish the gas filling when needed. The cause of this inconvenient attendant phenomenon is that the fluid pressure in the hydraulic lines drops below the fill pressure of the accumulator when the hydraulic equipment is idle, for example during intermissions between operations. However, as soon as this happens the floating piston will rest against the end of the accumulator on the fluid side and, with a further decrease in the pressure, there is developed a pressure gradient between the gas pressure in the accumulator and the fluid pressure in the connecting line to the hydraulic equipment. Should the fluid pressure drop completely to atmospheric, this pressure gradient may attain the order of magnitude of the fill pressure of the accumulator which, in the example selected, approximates 80 or 160 at.abs. Even a tiny leak, which may develop due to wear or contamination of the piston-sealing rings, then will cause gas to seep into the fluid line, leading to a pressure drop in the accumulator.

Another disadvantage of the floating piston-type hydraulic fluid accumulator, especially when such an accumulator is used in a horizontal position, is that sediments from the hydraulic fluid collect in the accumulator, such sediments including, for example, metal abrasions, contaminations and the like. These sediments may get under the piston-sealing rings when starting operation, damaging the sealing rings and thus making it possible for gas to seep through.

SUMMARY OF THE INVENTION This invention relates to hydraulic accumulators of the floating piston type and, more particularly, to a novel and improved accumulator including a dirt-stripping ring on the piston and improved-sealing means in an end position of the piston.

The objective of the invention is the provision of a floating piston for hydraulic fluid accumulators which prevents sediments from the hydraulic fluid from getting beneath the piston-sealing rings, will not allow the gas filling to escape due to damaged or contaminated piston-sealing rings, and which makes it impossible for the piston to impact on an end wall of the hydraulic accumulator.

In accordance with the invention, the floating piston is equipped, in addition to the conventional guiding and sealing rings, with an additional dirt-stripper ring. Furthermore, the face of the piston toward the hydraulic fluid end of the accumulator has a conical or frustoconical protrusion which, when the piston reaches the end wall at the fluid end of the accumulator, enters the opening in such wall provided for the fluid connection, and closes this opening gradually in further course of the piston motion. The bearing surface of the piston, rather than being formed in the conventional manner at the cylindrical portion of the piston, is formed at the base of the conical or frustoconical protrusion.

A stationary sealing ring which acts as a seal only when the piston is pressed against the fluid end of the accumulator cylinder by the gas pressure, is inserted into a countersurface in such end wall of the accumulator and around the hydraulic fluid inlet and outlet opening therein. When the piston is engaged with this sealing ring, the fluid facing end face of the piston and the end wall of the accumulator cylinder conjointly form an annular chamber which encloses a small residual amount of fluid. This serves as a liquid barrier against the gas in the accumulator, thus insuring the gas being sealed off hermetically.

An object of the invention is to provide such a floatingpiston-type hydraulic fluid accumulator in which the piston has, in addition to the conventional guiding and sealing rings, a dirt-stripper ring engageable with the internal surface of the cylinder.

Another object of the invention is to provide such a floating-piston-type hydraulic fluid accumulator having improved sealing means between the piston and a countersurface on the end wall of the cylinder, which is the end wall having the fluid inlet and outlet opening.

A further object of the invention is to provide such a floating-piston-type hydraulic fluid accumulator in which, when the piston is against the end wall of the cylinder having the fluid inlet and outlet opening therein, the piston and this end wall conjointly define an annular chamber enclosing a small residual amount of fluid serving as an hermetic gas seal.

For an understanding of the principles of the invention, reference is made to the following description of a typical embodiment thereof as illustrated in the accompanying drawing.

BRIEF DESCRIPTION OF THE DRAWINGS In the drawing, the single FIGURE is an axial sectional view through a hydraulic fluid accumulator, with a floating piston, embodying the invention.

DESCRIPTION OF THE PREFERRED EMBODIMENT As illustrated in the drawing, a hydraulic fluid accumulator includes an end wall I having a threaded fluid inlet and outlet opening 2 for connection to a hydraulic line. A housing cylinder 3 is threadedly connected to end wall 1, at one end, and to a cover 4, at the other end. Cover 4 is provided with a gas-filling valve 5 and a closure cap 6 for valve 5. A floating piston 7 is slidable axially in housing 3 and has sealing rings 8 and guiding rings 9 seated in grooves in its cylindrical peripheral surface.

In accordance with the invention, piston 7 has, additionally, a dirt-stripper ring 10 seated in a groove in a cylindrical peripheral surface, and its face toward wall I is formed with a conical or frustoconical, substantially central, protrusion or hump. A diametrically planar bearing surface 12, for piston 7,

surrounds protrusion 11. Bearing surface 12 is cooperable with an annular bearing surface 13 on the inner side of wall 1, surface 13 also lying substantially in a diametric plane. In further accord with the invention, bearing surface 13 is formed with a circular groove in which there is seated a sealing ring 14. A check valve 15 is built into end wall 1, and threaded opening 2, for inlet and outlet of fluid, is continued as a substantially smooth opening 16 toward the inner side of wall 1.

Housing end wall 1 defines a bowl-shaped concavity in its inner surface. Bearing surface 13 of end wall 1 is disposed directly around fluid inlet and outlet opening 16 and, as mentioned, a groove is machined in bearing surface 13 to receive sealing ring 14. As the sealing ring 14, there may be used an O- ring or else a groove ring specifically shaped for the purpose.

When the accumulator empties, piston 7 moves in a direction toward end wall 1. Upon piston 7 seating on end wall 1, conical protrusion 11 enters opening 16 to an increasing extent, thus throttling the return flow of the residual fluid remaining in the accumulator. The motion of piston 7 is thus slowed down, so that its impact on end wall 1 is attenuated, Bearing surface 12 of piston 7 rests against bearing surface 13 of end wall 1, and compresses O-ring 14 by the amount indicated at 17. Thus, O-ring performs its sealing function, closing off the entire accumulator hermetically.

The bowl-shaped concavity of end wall 1, and the corresponding end face of piston 7, are so shaped that an angular chamber 18 is conjointly defined thereby when piston 7 rests against bottom I. The contours of piston 7 in its contact-making position are indicated in dash-dot lines. A residue of the hydraulic fluid remains in chamber 18 after this chamber is sealed off by O-ring 14. This residual hydraulic fluid forms a liquid barrier against the gas in the accumulator, and thus safeguards the sealing effect provided by O-ring 14.

Check valve 15, built into end wall 1, prevents fluid sealed into chamber 18 from flowing back into the hydraulic connecting line. When the hydraulic equipment is again placed in operation, which means that the operating pressure of the hydraulic fluid rises, check valve 15 provides for flow of hydraulic fluid into chamber 18, thus making it easier for piston 7 to lift off of O-ring 14.

While a specific embodiment of the invention has been shown and described in detail to illustrate the application of the principles of the invention, it will be understood that the invention may be embodied otherwise without departing from such principles.

What is claimed is:

1. In a hydraulic accumulator of the type in which an elastically compressible and expansible gas cushion is separated from the hydraulic fluid by a floating piston having sealing and guiding rings engaged with the cylinder, the cylinder having one end wall formed with a substantially central hydraulic fluid inlet and outlet opening, the face of the piston toward the one cylinder end wall being formed with a frustoconical substantially central protrusion which, when the maximum amount of hydraulic fluid has been withdrawn from the cylinder, enters the fluid inlet and outlet opening under the influence of the gas cushion, and the one cylinder end wall defining a bowl-shaped concavity in its inner surface, the improvement comprising an annular groove in said piston adjacent said face thereof; and a dirt-stripper ring seated in said groove; said piston face being formed with an annular diametrically planar bearing surface around said protrusion sealingly cooperable with a diametrically planar countersurface means in said bowl'shaped concavity of said one cylinder end wall.

2. In a hydraulic accumulator cylinder, the improvement claimed in claim 1, in which said countersurface means further includes a stationary sealing ring set in said last-mentioned annular bearing surface and engageable by said firstmentioned annular bearing surface to act as a seal only when the annular bearing surface of said piston face is pressed against said second-mentioned annular bearing surface by the gas pressure. I

3. In a hydraulic accumulator cylinder, the improvement claimed in claim 1, in which said piston face, when pressed against said sealing ring, defines, conjointly with said bowlshaped concavity, an annular chamber containing a residual amount of hydraulic fluid serving as a liquid barrier against leakage of gas from said accumulator.

4. In a hydraulic accumulator cylinder of the type in which an elastically compressible and expansible gas cushion is separated from the hydraulic fluid by a floating piston having sealing and guiding rings engaged with the cylinder, the cylinder having one end wall formed with a substantially cen tral hydraulic fluid inlet and outlet opening, the improvement comprising an additional ring on said piston and constituting a dirt stripper; said one cylinder end wall defining a bowlshaped concavity in its inner surface; the face of said piston towards said one cylinder end wall being formed with a frustoconical substantially central protrusion which, when the maximum amount of hydraulic fluid has been withdrawn from said cylinder, enters said fluid inlet and outlet opening under the influence of the gas cushion; said piston face being formed with an annular bearing surface around said protrusion sealingly cooperable with countersurface means in said bowlshaped concavity of said one cylinder end wall; said countersurface means including an annular bearing surface cooperable with said first-mentioned annular bearing surface; said countersurface means further including a stationary sealing ring set in said last-mentioned annular bearing surface and engageable by said first-mentionedannular bearing surface to act as a seal only when the annular bearing surface of said piston face is pressed against said second-mentioned annular bearing surface by the gas pressure; said piston face, when pressed against said sealing ring, defining, conjointly with said bowl-shaped concavity, an annular chamber containing a residual amount of hydraulic fluid serving as a liquid barrier against leakage of gas from said accumulator; and a check valve in said one cylinder end wall providing for flow of hydraulic fluid from said fluid inlet and outlet opening into said annular chamber while preventing flow of fluid from said annular chamber into said fluid inlet and outlet opening. 

1. In a hydraulic accumulator of the type in which an elastically compressible and expansible gas cushion is separated from the hydraulic fluid by a floating piston having sealing and guiding rings engaged with the cylinder, the cylinder having one end wall formed with a substantially central hydraulic fluid inlet and outlet opening, the face of the piston toward the one cylinder end wall being formed with a frustoconical substantially central protrusion which, when the maximum amount of hydraulic fluid has been withdrawn from the cylinder, enters the fluid inlet and outlet opening under the influence of the gas cushion, and the one cylinder end wall defining a bowl-shaped concavity in its inner surface, the improvement comprising an annular groove in said piston adjacent said face thereof; and a dirt-stripper ring seated in said groove; said piston face being formed with an annular diametrically planar bearing surface around said protrusion sealingly cooperable with a diametrically planar countersurface means in said bowl-shaped concavity of said one cylinder end wall.
 2. In a hydraulic accumulator cylinder, the improvement claimed in claim 1, in which said countersurface means further includes a stationary sealing ring set in said last-mentioned annular bearing surface and engageable by said first-mentioned annular bearing surface to act as a seal only when the annular bearing surface of said piston face is pressed against said second-mentioned annular bearing surface by the gas pressure.
 3. In a hydraulic accumulator cylinder, the improvement claimed in claim 1, in which said piston face, when pressed against said sealing ring, defines, conjointly with said bowl-shaped concavity, an annular chamber containing a residual amount of hydraulic fluid serving as a liquid barrier against leakage of gas from said accumulator.
 4. In a hydraulic accumulator cylinder of the type in which an elastically compressible and expansible gas cushion is separated from the hydraulic fluid by a floating piston having sealing and guiding rings engaged with the cylinder, the cylinder having one end wall formed with a substantially central hydraulic fluid inlet and outlet opening, the improvement comprising an additional ring on said piston and constituting a dirt stripper; said one cylinder end wall defining a bowl-shaped concavity in its inner surface; the face of said piston towards said one cylinder end wall being formed with a frustoconical substantially central protrusion which, when the maximum amount of hydraulic fluid has been withdrawn from said cylinder, enters said fluid inlet and outlet opening under the influence of the gas cushion; said piston face being formed with an annular bearing surface around said protrusion sealingly cooperable with countersurface means in said bowl-shaped concavity of said one cylinder end wall; said countersurface means including an annular bearing surface cooperable with said first-mentioned annular bearing surface; said countersurface means further including a stationary sealing ring set in said last-mentioned annular bearing surface and engageable by said first-mentioned annular bearing surface to act as a seal only when the annular bearing surface of said piston face is pressed against said second-mentioned annular bearing surface by the gas pressure; said piston face, when pressed against said sealing ring, defining, conjointly with said bowl-shaped concavity, an annular chamber containing a residual amount of hydraulic fluid serving as a liquid barrier against leakage of gas from said accumulator; and a check valve in said one cylinder end wall providing for Flow of hydraulic fluid from said fluid inlet and outlet opening into said annular chamber while preventing flow of fluid from said annular chamber into said fluid inlet and outlet opening. 